FIX: ensures emoji helper is working with custom emojis (#7843)

app/helpers/emoji_helper.rb

@@ -7,7 +7,10 @@ module EmojiHelper
     str = str.gsub(/:([\w\-+]*(?::t\d)?):/) do |name|
       code = $1
 
-      if Emoji.exists?(code)
+      if code && Emoji.custom?(code)
+        emoji = Emoji[code]
+        "<img src=\"#{emoji.url}\" title=\"#{code}\" class=\"emoji\" alt=\"#{code}\">"
+      elsif code && Emoji.exists?(code)
         "<img src=\"#{Emoji.url_for(code)}\" title=\"#{code}\" class=\"emoji\" alt=\"#{code}\">"
       else
         name

app/models/emoji.rb

@@ -38,6 +38,11 @@ class Emoji
     Discourse.cache.fetch(cache_key("tonable_emojis")) { db['tonableEmojis'] }
   end
 
+  def self.custom?(name)
+    name = name.delete_prefix(':').delete_suffix(':')
+    Emoji.custom.detect { |e| e.name == name }.present?
+  end
+
   def self.exists?(name)
     Emoji[name].present?
   end